1. Field of the Invention
The present invention relates to a rotation angle detection technique for detecting the rotation angle of a rotating body by using a magnetic sensor and to a part mounting apparatus using this technique.
2. Background Art
A variety of mechanisms have been suggested for detecting the rotation angle of a rotating body that rotates about a rotation axis. For example, Japanese Patent Application Publication No. 2007-155482 describes a rotation angle detection device in which the rotation angle of a follower that rotates following the rotation of a steering wheel is detected by using a MI (Magneto-Impedance) sensor. In such a rotation angle detection device, a magnet is attached to one end of the follower, and the MI sensor is disposed to face the magnet from the rotation axis direction. The MI sensor outputs a signal of a value corresponding to the rotation angle of the magnet that rotates integrally with the follower. Therefore, the rotation angle of the follower can be reverse calculated from the output signal of the MI sensor.
However, the output signal of the magnetic sensor such as a MI sensor changes depending not only on the rotation angle of the magnet but also on the distance between the magnetic sensor and the magnet. Thus, where the distance between the magnetic sensor and the magnet changes, the magnetic sensor outputs signals of different value even if the rotation angle of the magnet is the same. Therefore, in configurations in which the rotating body not only rotates about a rotation axis, but also moves in the rotation axis direction, the rotation angle of the magnet cannot be accurately determined from the output signal of the magnetic sensor. As a result, the detection accuracy of the rotation angle of a rotating body is sometimes decreased.